System and method for browsing hierarchically based node-link structures based on an estimated degree of interest

ABSTRACT

Method and system to enable a user to view large collections of hierarchically linked information on a computer based display. A tree structure visualization is created which presents a representation of the complete collection of information on the display. The visualization fits completely within a fixed area of the computer based display, negating the need to scroll information into the display area. The visualization is based on identified focus nodes and through calculation of a Degree of Interest (DOI) for each of the nodes based in the structure. Layout and presentation of the visualization structure is based on the DOI values in combination with considerations of available display space. A user may dynamically manipulate views of the structure by selecting one or more focus nodes, thus causing a recalculation of the degree of interest.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of informationvisualization and in particular to the display of representations oflinked information based on user interest.

BACKGROUND OF THE INVENTION

[0002] Many applications of computers to practical problems involve thedisplay of representations of linked information such as hierarchicaldata. Linked information refers to information that has some logical ororganizational relationship. Examples are organization charts, computerprograms, Web sites, filing systems, or biological taxonomies. Thesedata structures are often much larger than will conveniently fit on thescreen of a computer display monitor so that information can be easilyextracted. But finding a way of presenting these structures to userssuch that (1) they can find elements in the structure quickly and (2)they can understand the relationship of an element to its surroundingcontext is an important enabler to many uses of such data.

[0003] One example is in the area of linked hierarchical data. Linkedhierarchical data is often displayed in a tree structure. Several typesof methods have been used to display such tree structures:

[0004] (1) Uniform layout of trees. Trees can be laid out uniformly. Thenumber of nodes at the leaves of all the subtrees is computed andmultiplied by an amount of space per node plus spacing between nodes andbetween subtrees. Then the nodes are scaled so that this fits across thedisplay. This method works for small trees, but any attempt to portray atree structure of moderate size, say 600 nodes, scaled to the width of adisplay will have the approximate appearance of a horizontal line, sincethe width increases exponentially while the height increases onlylinearly.

[0005] (2) Compressed layout of trees. The space required for the treecan be opportunistically compressed by sliding portions of deepersubtrees underneath shallow subtrees. If the tree has uniform depth,this is of no help. If the depth is non-uniform, more nodes can beaccommodated in the same space, but this technique is only a limitedimprovement and cannot handle very large trees.

[0006] (3) Treemaps. Treemaps are described by Johnson, B. andShneiderman, B. in the publication entitled “Treemaps: A space-filingapproach to the visualization of hierarchical information structures”,Proceedings of IEEE Information Visualization '91, 275-282. Treemaps isa technique in which lower subtrees are contained within higher nodes ofthe tree. A space is divided, say vertically, into a number of sectionsequal to the number of branches. Each section is then dividedhorizontally according to the number of branching at the next level downin the tree. The next level is then divided vertically again and so onalternating between vertical and horizontal definition of the spaceuntil it is too small to divide. Since creating a tree in this way doesnot allow any room for the content of nodes, the technique can bemodified so that each division has extra space to be devoted to the nodecontents. This technique stays within predetermined space bounds, but asnodes become smaller and smaller they no longer have room for content(except for maybe a uniform color), the aspect ratios of the nodes varywidely, obscuring simple relationships.

[0007] (4) Techniques of variable manual expansion. Some techniquesallow the user to choose which nodes are displayed. In this way, thereneed not be space for all nodes at the same time and those visible areones more interesting to the user. One such technique was introduced inby Engelbart, D. C. and English, W. K. , “A Research Center forAugmenting Human Intellect”, AFIPS Conference Proceedings of the 1968Fall Joint Computer Conference, San Francisco, Calif., December 1968,Vol. 33, pp. 395-410 (AUGMENT,3954,). Republished in Computer SupportedCooperative Work: A Book of Readings, Irene Greif [Editor], MorganKaufmann Publishers, Inc., San Mateo, Calif., 1988, pp. 81-105. The userindicates the higher and lower level numbers of the tree to be expanded.This technique allows the user to look horizontally across a treestructure. For example, a user might look at all the procedure call andvariable declarations in a program, while suppressing the code itself,which resides at lower levels in the tree. The limitation of thistechnique is that there is no guarantee the tree will all fit on thedisplay in any of these views and the user cannot expand one part of thetree, but not another. So the technique is usually paired withscrolling.

[0008] Another example of such a technique is used in the user interfaceof the Apple Hierarchical Filing System used on computer systemsavailable from Apple Computer, Inc. of Cupertino Calif. Each level inthe tree can be expanded individually by clicking on a small triangle tothe left of the level. Thus the user can expand portions of the treethat are to be compared on the screen, while keeping other portions ofthe tree compressed by eliding nodes below the compressed subtree root.But this technique also needs to be paired with scrolling andconsiderable manual manipulation must be performed by the user toconstantly adjust views.

[0009] (5) Fish-eye Views. Fish-eye views were described by Furnas, G.W. (1981/1999), in the publication “The FISHEYE View: A new look atstructured files”, reprinted in Card, S. K., Mackinlay, J. D.; andShneiderman, B. (eds.) (1999), Information Visualization: Using Visionto Think. San Francisco: Morgan-Kaufmann. Fish-eye views describes aclass of techniques in which nodes are displayed or elided according tothe user's computed degree-of-interest (DOI) in them. The estimated

DOI of a node=Intrinsic Importance+Distance from a focus node.

[0010] The Intrinsic Importance of a node is its distance from the rootand the Distance of a node is the number of nodes that must be traversedby following parent and child links from the node of interest untilreaching the subject node. All those nodes whose DOI lies below acertain threshold are not displayed. If the user indicates interest insome node, say by selecting it, this calculation is performed and thedisplay elides those nodes below the threshold. In this way, the displayof the tree follows the user's changing interest. The problem with thistechnique is that there is no guarantee the displayed trees will fit inany display bounds, thus wasting useful information space. The techniqueis especially problematic when there are a large number of sibling nodesin the tree.

[0011] (6) Focus+Context Displays. Focus+context displays are variantsof fish-eye views that use various sorts of techniques to devote morespace or detail of the display to some areas of interest, compressingother parts of the displayed structure to mainly support the context ofthe focus elements and showing the user where to select to navigate to anew position in the structure. One example of a focus+contexthierarchical structure is cone-trees (see Robertson, G. G., Mackinlay,J. D. and Card, S. K. (1991). Cone trees: Animated 3D visualizations ofhierarchical information. Proceedings of CHI '91. ACM Conference onHuman Factors in Computing Systems New York, 198-194.). Cone-treesarrange the nodes in a 3-D tree. Selecting a node rotates a branch ofthe cone-tree, bringing related nodes into the foreground while sendingother nodes into the background. This technique uses natural perspectiveto achieve some of the effect of Furnas's fish-eye views. Furnas'fish-eye view technique can be combined with cone-trees, thus allowingthe display of larger trees. Because this is a 3-D display, some of thenodes occlude each other.

[0012] (7) Hyperbolic Trees. In hyperbolic trees the space itself isstretched according to a hyperbolic projection (see Lamping, J. and Rao,R. (1994), “Laying out and visualizing large trees using a hyperbolicspace”, Proceedings of UIST '94, ACM Symposium on User InterfaceSoftware and Technology, 13-14). An implementation of a hyperbolic treestructure visualization is available from InXight Software, Inc. ofSanta Clara, Calif.). Selecting a node moves it to the center (or side)of the display. Nodes further out are smaller and closer to each other.The display stays within fixed boundaries. But only a limited number oflinks out from the focus node can be seen. Moreover, it is morecomplicated to model complex user's DOI.

[0013] Despite such methods and techniques there remains a need toeffectively display and extract useful information from large bodies oflinked data.

SUMMARY OF THE INVENTION

[0014] The present invention provides for user browsing of largecollections of linked information on a computer-based display. Avisualization is created which presents a representation of the completecollection of information on the display. The visualization fitscompletely within a fixed area of the computer-based display, negatingthe need to scroll information into or out of the display area. Thevisualization is based on identified focus nodes and through calculationof a Degree of Interest (DOI) for each of the nodes in the structure.Layout and presentation of the visualization structure is based on theDOI values in combination with considerations of available displayspace. A user may dynamically manipulate views of the structure byselecting one or more focus nodes, thus causing a recalculation of thedegree of interest.

[0015] The present invention may be used to display information unitscomprised of data items that are static, dynamic or a combination ofboth static and dynamic. An example of information units having staticdata items would be the nodes in an organization chart. An example of aninformation unit having dynamic data would be the representation of aweb site wherein an information unit represents a web page within thesite and includes a dynamic data item representing the number of “hits”that corresponding page is encountering over-some period of time.

[0016] The method of the present invention is generally comprised of thesteps of identifying a focus node for plurality of nodes representing acollection of hierarchically linked information; generating a degree ofinterest value for each of said plurality of nodes, said degree ofinterest value relative to said focus node and corresponding to a nodesize; laying out in a tree structure said plurality of nodes positionedbased on associated links and sized based on associated degree ofinterest values; identifying and performing any node compressionnecessary for displaying said hierarchically linked information based onthe layout of said plurality of nodes; and displaying saidhierarchically linked information based on said layout of plurality ofnodes and node compression.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a flowchart of the basic steps for creating avisualization of a linked structure in the present invention.

[0018]FIG. 2 is an illustration of a DOI tree of uniform structurehaving the root node as the focus node as may be displayed in thecurrently preferred embodiment of the present invention.

[0019]FIG. 3 is an illustration of the DOI tree of FIG. 2 with the focusnode moved to a second level node, as may be displayed in the currentlypreferred embodiment of the present invention.

[0020]FIG. 4 is an illustration of the DOI tree of FIG. 2 with the focusmoved to a leaf node so that it becomes the new focus node, as may bedisplayed in the currently preferred embodiment of the presentinvention.

[0021]FIG. 5 is an illustration of a DOI tree showing various treecompression techniques, as may be utilized and displayed in thecurrently preferred embodiment of the present invention.

[0022]FIG. 6 is an illustration of various predetermined areas in adisplay area, as may be utilized to display a DOI tree in the currentlypreferred embodiment of the present invention.

[0023]FIGS. 7 and 8 are illustrations of the DOI tree of FIG. 2 with andwithout using the Expand to Fit techniques of the currently preferredembodiment of the present invention.

[0024]FIG. 9 is an illustration of a large organization chart as may bedisplayed by the currently preferred embodiment of the presentinvention.

[0025]FIG. 10 is an illustration of a representation of a large databasewith a leaf node being located as the subject of a search and thus beingdisplayed as a focus node, as may be displayed in the currentlypreferred embodiment of the present invention.

[0026]FIG. 11 is an illustration of a tree derived from a database withmultiple links per node, wherein one node is used to generate the treestructure and other links become visible upon some user action, as maybe displayed in the currently preferred embodiment of the presentinvention.

[0027]FIG. 12 is an illustration of a biblioplex showing multiplegenerations of linkages from a main document, as may be displayed in thecurrently preferred embodiment of the present invention.

[0028]FIG. 13 is an illustration of a control panel for controlling theDOI tree visualization of the currently preferred embodiment of thepresent invention.

[0029]FIG. 14 is a block diagram illustrating the functional softwareimplemented components and data flow as may be used to implement thecurrently preferred embodiment of the present invention.

[0030]FIG. 15 is a block diagram of a computer-based system as may beutilized to implement the currently preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention provides an information visualizationtechnique that enables a user to effectively browse through largecollections of linked data. When utilizing the present invention a useris able to dynamically manipulate views of large amounts of displayeddata so that the information presented is effectively perceived by theviewer. The present invention may be used to display information unitscomprised of data items that are static, dynamic or a combination ofboth static and dynamic. An example of information units having staticdata items would be the nodes in an organization chart. An example of aninformation unit having dynamic data would be the representation of aweb site wherein an information unit represents a web page within thesite and includes a dynamic data item representing the number of “hits”that corresponding page is encountering over some period of time.

[0032] The present invention operates on linked information, which canoften be represented as a node-link structure. In a node-linkrepresentation, each node represents an information unit and the linkrepresents a relationship amongst the different nodes. The underlyingdata may have some actual linkage (e.g. web pages or other documentscontaining hypertext links) or some logical linkage (e.g. the nodescomprising an organization chart).

[0033] The present invention has been implemented for operation oncomputer based systems having a graphical user interface such as thoseutilizing the Windows® Operating System form Microsoft, Inc. or the MacOS operating System from Apple Computer, Inc. Such graphical userinterfaces have the characteristic that a user may interact with thecomputer system using a cursor control device and/or via a touch-screendisplay, rather than solely via keyboard input device. Such systems alsohave the characteristic that they may have multiple “windows” whereindiscrete operating functions or applications may occur. A more completedescription of such a computer-based system upon which the presentinvention may be implemented is provided below.

[0034] Conceptual Framework

[0035] The present invention combines (a) the idea of computing DegreeOf Interest (DOI) estimates of users' interest with (b) focus+contexttechniques for dynamically changing the view as the DOI changes and (c)adjustment of what is displayed based on available display resource(e.g. the viewable area of a computer display, or the size of a “window”on the display).

[0036] The present invention can be thought of as being modular so thatthe display of information to the user is computed in two parts: (1) anestimation of users' degree-of-interest in each of the nodes and (2) avisualization of the data based on the computed users' interest and theamount of available display resource. A visualization using the presentinvention may be used to present various visualizations of linkedinformation such as tree structures or collections of hyper-linkeddocuments. The present invention further uses animation to provide forsmooth visual transitions to indicate changes of DOI in the displayedstructure.

[0037] (1) Estimate of users' degree-of-interest in nodes

[0038] The Degree of Interest (DOI) refers to a value attributed to aparticular node with respect to some focus node. The DOI value providesa way of placing a quantitative value on the nodes. The DOI value may becalculated in many different ways, and is often directly related to themanner in which the data to be visualized is captured. For example, realtime usage data may be used to calculate a DOI so the DOI value could bebased on the usage.

[0039] In the prior art, the DOI of a node in a tree structure isestimated as the Intrinsic Importance plus the Distance from a focusnode. The Intrinsic Importance represents the relevancy or importance ofa node with respect to a root node and is measured as the number ofnodes from the root node to the subject node. The Distance of a nodefrom the focus node is the number of nodes that must be traversed byfollowing parent and child links from the node of interest untilreaching the subject node.

[0040] In the present invention, the degree of interest calculation fora tree structure is different from that disclosed in the prior art. Inthe prior art, all siblings' nodes that are the same distance from thefocus node have the same DOI value. The calculation of the presentinvention treats the children of a parent node as ordered and assignsfractional DOI offsets to the children based on order distance from thefocus node. The farther the sibling is from the focus node based on theordering, the more the fractional decrement in its DOI (but thedecrement is always less than 1). Further, the DOI of the children ofthe siblings is based on the siblings DOI. This allows the visualizationelement to decide which sibling nodes to compress and how to compressthem.

[0041] (2) Visualization

[0042] As noted above, various visualization techniques may be used whenimplementing the present invention. Initially, each DOI valuecorresponds to a node size parameter. Typically, this node sizeparameter may correspond to a largest node size for a particular rangeof DOI values. Upon generation of the structure in the visualization,the nodes are laid out using the node size parameter along with anystructure-based adjustments. These structure-based adjustmentsfacilitate optimal use of the display area in terms of presentinginformation, as well as providing a smoother visual appearance of thestructure. Further visualization compressions of the nodes in thestructure may be made based on the available display area. For example,portions of the structure lying in predetermined areas may beaggregated, or certain portions of the structure may be collectivelyrepresented by a symbol as a result of their lower DOI values (whereinthe size of the symbol may represent the number of nodes beingrepresented). Alternatively, a displayed structure may not completelyutilize a display resource, so visualization expansions may occur tomore effectively utilize the available display resource.

[0043] Currently Preferred Embodiment

[0044] The currently preferred embodiment of the present invention isimplemented to display hierarchically linked data in a tree structure.This is hereinafter referred to as a Degree of Interest (DOI) Tree. TheDOI tree can be used to display various types of hierarchicalinformation such as organization charts, file structures, orrepresentations of web sites.

[0045] The following terminology is used to describe a tree structure. Aroot node refers to the topmost node in the structure and the one inwhich the rest of the tree structure emanates from. A tree structurewill have multiple levels, each level representing a horizontal portionof the structure. The nodes in the tree structure will be connected vialinks. Nodes will have relationships with other nodes, which are termedparent, child or sibling. A node is a parent node to another node if itis directly linked and is one level above the other node. Similarly, anode is a child node if it is directly linked and is one level below theother node. Sibling nodes are those that lie on the same level and whichhave the same parent node.

[0046]FIG. 1 is a flowchart that describes the general method of thepresent invention. First, node information is generated for nodes in thevisualization, step 101. This node information is generated using storeddata for the nodes. A focus node is then determined, step 102. Upon thefirst display of the visualization, the focus node may be the “root”node, or it could be based on how display of the structure wasrequested. During browsing of the structure, the focus node wouldtypically be identified by user selection of a particular node. The DOIfor the nodes are then generated, step 103. As described above, the DOIis determined not only by the distance from the focus node, but alsobased on it's (or it's parent's) order with respect to the focus node.The nodes are then sized and laid out based on their DOI value, step104. A manner in which nodes are sized is provided below with respect topseudo code provided in Table 1. The manner in laying out the nodes isbased on the visualization structure (e.g. a tree or some otherstructure). Visualization adjustments are then made to optimize use ofthe display area, step 105. As noted above, these visualizationadjustments may be visualization compressions or visualizationexpansions. The visualization structure is displayed, step 106. When anew focus node is selected and detected, step 107, the steps repeatstarting at step 103 with the new visualization structure preferablybeing displayed using animation techniques.

[0047] Table 1 provides pseudo-code that describes the manner ofprocessing nodes in the currently preferred embodiment. TABLE 1Pseudo-Code For Processing Nodes (recursive for all nodes) if focus node(i.e DOI=0), set to large size else if DOI value > −1 and <0 set tolarge size adjusted by fade value else if DOI value > −2 and <=−1 set tomedium size adjusted by fade value else if DOI value > −4 and <=−2 setto small size else elide display of node

[0048] Referring to Table 1, the listed operations are repeatedrecursively for each node. Generally, the focus node will have thelargest possible size, with smaller sizes being assigned based on theDOI value. The numerical values presented in Table 1 are forillustration and are actually parametric thresholds that could vary.Note that the node sizes are assigned based on DOI values falling withina particular range. Use of other values or parametric thresholds wouldnot cause departure from the spirit and scope of the present invention.The option of a fade value is a technique for making small distinctionsamong nodes that would otherwise be the same size. The fade value is afractional value used to decrease the size of nodes as they get furtheraway from the focus node. For examples for a hierarchical structure afade value of 0.10 would decrease the size of the row of nodes above andbelow the focus row by 10%. The next row above and below that rose wouldbe 20% smaller. This permits more space for the focus node for largetrees with many levels.

[0049] It should also be noted from Table 1 that if a DOI value fallsbelow some particular threshold, here <−4, then the node will be elided(i.e. not displayed).

[0050] Calculation of the Degree of Interest

[0051] The basic calculation of the Degree of Interest (DOI) for nodesin using the standard layout follows the following rules:

[0052] 1. The Focus nodes and parent nodes up to the root node areassigned a DOI value of 0.

[0053] 2. Assign a DOI value of −1 plus offset to sibling nodes of nodeshaving a DOI value of 0.

[0054] 3. For the rest of the nodes, assign a DOI value of one less thantheir parent node.

[0055] The standard layout is one where there is a single focus node. Inan alternative scheme where there may be multiple focus nodes (e.g.nodes found as a result of some search) the rules for assigning the DOIwould be as follows:

[0056] 1. Assign a DOI value of −1 to all selected nodes;

[0057] 2. Assign a DOI value of −1 to parents of selected nodes up toroot node.

[0058] 3. For the rest of the nodes, assign a DOI value of one less thantheir parent node.

[0059] With respect to the offset described above, the DOI calculationof the present invention treats the children of a parent node as orderedand assigns fractional DOI offsets to the children based on orderdistance from the focus node. The farther the sibling is from the focusnode based on the ordering, the more the fractional decrement in its DOI(but the decrement is always less than 1).

[0060] Visualization of the DOI Tree

[0061] For the visualization of the DOI tree, there are a small numberof possible node sizes for presenting the information associated withthe node. For most tree structures, it has been determined that three isa reasonable number of nodes sizes, but utilization of five or someother number of node sizes would not cause departure from the spirit andscope of the present invention. As described above with respect to thegeneral concepts, the particular node size used depends on the DOI ofthe node. A table may be used to map DOI values into node sizes duringthe creation of the visualization. The table may contain actual nodesizes, or sizing factors for use in drawing each of the nodes.

[0062]FIG. 2 shows the display of a uniform tree of 4 levels, with 4branches at each level and the focus on root node 201. The root node 201has been selected for the focus node and automatically has a largersize. To further indicate that it is a focus node, it may be displayedso that it is more visually distinct, e.g. in a different color than theother nodes. Smaller node sizes have been automatically selected fornodes with lower DOI. For example, nodes at level 202, level 203 andlevel 204 are represented as consecutively smaller. It should also benoted that in FIG. 2, because of display space constraints, thecollections of nodes at level 205 (below level 204) are collectivelyrepresented as a triangle. In the currently preferred embodiment, thehighest DOI is 0, the lower DOIs are negative numbers.

[0063] In FIG. 3, a node 301 of the tree displayed in FIG. 2 has beenselected. The node 301 is on the next level down, and selection causesthe changing of the DOI calculation for the nodes. When the tree isdisplayed, node 201 is reduced in size and child nodes 302 below the newfocus node 301 in the tree are increased in size, according to thecomputed DOI's for the nodes. Although not illustrated, preferably thetransition proceeds by a smooth animation from one state to another. Ithas been determined that such animation is desirable in order to keepthe user oriented and unconfused about the transition and change infocus nodes.

[0064] Referring to FIG. 4, a user has selected one of the lowest nodes401 either by selecting directly, or by selecting nearby nodes, causingthe focus node 401 to get larger, and be more easily selectable. Notethat other nodes have been re-sized based on their DOI value. Forexample, nodes 402 and 403 have increased in size, while nodes 301 and201 have decreased in size. Again, this would be presented to a user viaan animated transition.

[0065] Node Layout

[0066] The method for layout of nodes is as follows. There is a fixedoriginal size for several incremental sizes of nodes. The tree is laidout at those sizes as if there were infinite space available. If theheight of the tree is larger than the height of the window, a scalefactor is calculated so that it will fit vertically. The method thendetermines actual node sizes multiplied by the scale factor and lays outscreen positions based on those sizes. When there is not enough spacehorizontally for the nodes at a certain level, space is allocated forthe focus node and for its parents and then to their siblings in orderto the right and left of the focus node until a certain percentage ofthe horizontal space is left. Then the horizontal space for the rest ofthe nodes and the subtrees below them is compressed uniformly. That isthe subtree below each sibling node will be compressed horizontally sothat it fits below the sibling node.

[0067] Node Compression

[0068] It has been determined that it is desirable to always displaysome representation of the complete tree in the available display area.However, the display area for the tree on the display is generally afixed resource. Accordingly, the tree needs to be constrained in ways tostay within its resource. The basic DOI-based display technique verygreatly reduces the pressure on that resource. Even with the techniquedescribed so far, it is possible for all the nodes not to be effectivelypresented on the screen. There are two cases to consider, the tree notfitting in the horizontal direction and the tree not fitting in thevertical direction. The tree not fitting in the horizontal direction iscommon and occurs either because of a large branching factor below onenode or because, since trees increase in width exponentially, there isan accumulation of widths.

[0069] If the number of nodes across is large because of theaccumulation of several branches, these are specially handled becausethe nodes below each box are laid out in the horizontal space availablefor each box. This pattern is visible in the tree illustrated in FIG. 5.If the branching factor is large, then the nodes are folded as for nodegroups 501 and 502 illustrated in FIG. 5. Folding refers to a techniquewherein a node group is organized so that part of it is moved verticallybelow another part. If there are elided nodes below a threshold DOIvalue, then a triangular symbol, which will have a size proportionate tothe log of the number of nodes, is used. Such a symbol is triangle 503as shown in FIG. 5.

[0070] If the number of nodes across the display at any level is large,the available display resource into which the nodes are to be displayedis vertically divided into three regions as illustrated in FIG. 6.Referring to FIG. 6, a regular free layout zone 601, a compression zone602, and an aggregation zone 603 are displayed. Typically 70% of thescreen is in the free layout zone 601, with 20% in the combinedcompression zones 602, and 10% in combined aggregation zones 603. Ifnecessary, the horizontal layout may be compressed for some of thenodes, for example by overlapping them. This is illustrated by level 504of FIG. 5. In the currently preferred embodiment, as a cursor controldevice is moved over these nodes they spring to the front, overlappingtheir neighbors, thereby allowing the user to peruse them. When themaximum compression is reached, an aggregate representation will be madefor the remaining nodes, such that selecting in this region will selectthat node proportionate to that region. For example, if 100 nodes are inthe aggregation region, selecting 30% of the way to the edge of thedisplay would select the 30^(th) node from the inward edge of theregion.

[0071] Table 2 contains pseudo code that describes the laying out of avisualization structure where nodes are compressed, in greater detail.TABLE 2 Pseudo Code For Laying Out Visualization Structure Set X(horizontal) and Y (vertical) display screen positions for each node:calcExtents to determine total width necessary to layout chartrecursively calculate total width of each level of hierarchy calculateunlimited width position for each node in x direction save maximum widthof each subtree and whole tree assign y position of each node (row)setFinalPositions to assign final x positions to the children of currentnode if sufficient room available or compression factor already setnormalLayout - for each child of the current node calculate normal xspacing (adjust by compression) setFinalPositions again for each childof current one else sort child list in order of DOI + localDOI valueassign 70% of available x space in sorted list order calculatecompression factor for the rest of the subtrees set final x positions ofeach node setFinalPositions on the children of each node (compressed)determine next appropriate scale factor to fit within current displayarea setXYs again using new scale factor if scale factor for display haschanged adjust old node size values for displayed nodes using new scalefactor

[0072] The nodes with the highest DOIs at a level have the largest nodesize, (for example see node 401 of FIG. 4). This node size establishesthe vertical height of a region in which to lay out the immediatedescendents of all the nodes at that level. If there are too manydescendents horizontally, the descendents are folded into multiple rows.Such folding into multiple rows is a common organization chartconvention (with a vertical line joining the rows).

[0073] The localDOI value refers to the value at each level of the treethat determines priorities for horizontal space at that level only. Thisvalue could also be used for minor variations in the size of siblingnodes at one level.

[0074] The use of DOI to do selective node expansion (as describedbelow) and the use of folding rows greatly increases the size of a treethat can be horizontally laid out. Further, the use of compression andaggregation zones permits all trees to be fit within a fixed displayspace. It can also happen that a tree would be too deep vertically tofit within its space. In this case, nodes are either elided lower in thetree or in the middle, depending on the DOI. The term elide or elided istaken to mean that the nodes are not displayed and not that the node orits underlying data is deleted. First, a threshold DOI is established soif the nodes for a tree are less than the threshold DOI, then they areelided and replaced by an elision graphic. Since nodes decrease inelliptical importance with distance from the root and in distanceimportance with distance from the focus node(s), then a very deep treewould tend to show some nodes around the root and some nodes around thefocus node, typically causing some of the intermediate nodes to beelided. However, the currently preferred embodiment provides forcreation of the elision graphic above a node at a certain distance abovethe focus node. The elision graphic would represent nodes elidedincluding the root node. The width of the symbol is proportional to thelog of the number of nodes represented. The number of levels above thefocus to display may be controlled by a variable specified by the user.

[0075] When the DOI is lower for the lower part of the tree, as happensfor subtrees being fit within a node height or which would hit thebottom of the display area, the lower part of the tree is replaced by anappropriately proportioned elision graphic, e.g. a triangle whose widthis proportional to the log of the tree width and whose height isproportional to the tree depth.

[0076] Node Expansion

[0077] It can be that as in FIG. 2, the use of the techniques describedso far may leave unused space in the display area. Therefore, thepresent invention provides for a user to expand part of the tree intothis unused space. Unused space commonly results from an upper limit onnode size which causes the tree to take up less vertical space than isavailable in a typical window. It has been determined that enlarging tofit vertically would cause the nodes to become unusually large andappear to be distorted. Further, it would limit horizontal space, whichit has been found to be more crowded.

[0078] Node expansion occurs when there is still vertical spaceavailable on the display. Expansion occurs on the “most interestingnode”. The number of levels below the focus node to expand automaticallycan be controlled by the user. A practical limit has been found to bethree or four levels. The limit is necessary to prevent a very deep treefrom scaling so that all of the nodes become too small. Node expansionat each level will occur on the “most interesting node”.

[0079] Table 3 provides pseudo code describing such node expansion:TABLE 3 Pseudo Code For Node Expansion Find current node to be expandedfind most interesting child of current node for each child of currentnode set localDOI to lower value as move away from most interesting onedecrement node fade value if this is most interesting node,expandDescendants of this node else markDescendants as above with lowerDOI and fade values

[0080] The tree is automatically expanded below the focus node bychoosing the node in the level below with the most descendants. The nextlevel below that node is expanded in the same way until the entire depthof the tree is shown or the user-specified number of levels is reached.This is done whenever the user chooses a new node to focus on whichshows the expansion of the branch of the tree with the current node. Thenodes selected at each level to expand form a “spine” of nodes that arerepresented in the large size about twice as large as their medium sizedsibling nodes. This allows room for the display of the tree structurebelow the siblings using the smallest size nodes. Because the size ofthe nodes in the spine of this expansion are nearly the same, a “fade”value is used to make all of the nodes smaller at each level away fromthe current focus. This prevents the automatic scaling from making allof the nodes too small for very deep trees. The nodes close to the focusare thus always displayed in a relatively large size.

[0081] There are several ways for determining or otherwise identifyingthe “most interesting node” to expand. This can be an automated processor one based on user input. Some examples are: (1) This could be thenode with the highest DOI on a level, or (2) it could be a nodeidentified based on user supplied search terms.

[0082]FIGS. 7 and 8 illustrate the tree of FIG. 2 expanded according tothe subtree with the most nodes. Referring to FIG. 7, the tree does nottake up the entire display area, as illustrated by the unused area 701.Referring to FIG. 8, the node 801 and descendants comprise the subtreewith the highest number of subnodes. At the level 802, the node 801 andits subtree has been expanded. This continues so at level 804, the node803 and its subtree is expanded and at level 806 the node 805 and itssubtree is expanded. As illustrated, the node expansion continues untilthe bottom nodes or “leaves” of the tree are reached.

[0083] It should be noted that node expansion is a slight departure fromthe basic general concept described above. However, node expansion hasbeen found to be very useful in that it often provides insights intosearch levels beyond what would normally be provided (as many as 6levels). This could dramatically decrease search times for particularinformation.

[0084] Data Item Information Display

[0085] Each node typically has a number of data items to be displayed.For example, for an organization chart, the data items to be displayedcould include fields such as Post, Post it reports to, Name, Title,Office extension, Email, Picture file link, Home page link, etc. Thelarger the number of data items to be displayed, a bigger displaysurface area for a node is needed. For the focus node, the majority ofthe information may be displayed.

[0086] As discussed above, nodes will typically be of different sizes.As nodes get smaller, there is less room to display this information.Information displayed on the nodes is ranked by priority and as thenodes have less space the items with the higher priority are displayed.The present invention provides several techniques to allow theinformation to fit on a node:

[0087] 1. Data deletion. Smaller nodes only display some of the dataitems.

[0088] 2. Word abbreviation. Words and phrases are abbreviated if thereis not room on the line where they are displayed. Different textabbreviation rules are applied according to the type of information(Names, phone numbers, email addresses). A substitution table is alsoread from a file to substitute abbreviations for common words whenneeded. For example, Vice President becomes V.P.

[0089] 3. Node rotation. The normal view of nodes shows them as 3D boxes(illustrated in FIG. 10). Using a gesture such as dragging the cursorleft or right on a box makes the boxes appear to rotate such thatanother face of the boxes is now in the front. This allows more dataitems to be presented. Software based programming techniques forperforming such node rotation to present different information is wellknown in the art.

[0090] It should also be noted that all or some of these techniquescould be utilized. Alternatively, another window could be displayedalongside the structure to display all of the information.

[0091] Animation of Tree Transitions

[0092] User orientation in the tree is preserved by making the views ofthe tree animate into each other. The animation time is set at adesirable level, usually in the range of (0.7˜1.0 sec) (see Card, S. K.,Moran, T. P. and Newell, A., The Psychology of Human ComputerInteraction, Hillsdale, J. M: Erlbaum (1983)). The average draw time perframe for recent frames is used to set the number of animation framesthat can be drawn in this time. This is used to calculate the in-betweenpositions of the boxes.

[0093] A tree transition is calculated based on a begin state and an endstate of the tree. Generation of an end state is initiated, for exampleby a user selecting a new focus node.

[0094] Applications

[0095] The present invention has been applied in providing aninteractive browser of node-link structures. The invention could beapplied in a variety of contexts in which node-link structures arevisualized. In particular, the invention could be applied in visualizingweb-related structures such as the structure formed by a cached set ofweb pages or other web objects.

[0096] More generally, the invention could be applied to provide abrowser for organization charts, file system hierarchies, hypertexthierarchies, world wide web connectivity structures, parts breakdowns,SGML structures, or any other large node-link structures. The browsercould be used in editing structures or their contents.

[0097] Items in the tree can be linked to arbitrary Uniform ResourceLocator (URL) pages or to programs, such as an email program. Hence, thetree can act as a browser to initiate display of web data. The tree as abrowser operates more quickly than a conventional web browser, because agroup of the pages can be viewed on the screen together and theirrelationship with other pages shown.

[0098] Described below are possible applications.

[0099] (1) Organization Chart. One use of this is for organizationcharts in which the nodes serve as links to supporting data as in FIG.9. This chart has over 400 nodes, is accessible over the Web, andcombined all the information contained in 12 separate organizationcharts (each of which filled a page). By searching for a name or bybrowsing the chart, the details of the individual organizations isrevealed. Furthermore, the chart serves as a gateway into theorganizational home pages of the different organizations (accessed byclicking the appropriate link within the node). It also can be used toaccess email to any of the individuals whose email is given on the chartby simply clicking the link.

[0100] (2) Web Sites. Another use is for views of Web sites, which havebeen coerced or otherwise reduced into tree form. Thumbnail miniaturesof pages can be displayed in the nodes. Full size displays of the pagescan be displayed alongside the tree using a suitable web browsingapplication.

[0101] (3) Web site statistics. The DOI of individual pages in a website can be set to a function of the number of hits that page hasreceived in some predetermined interval of time such as the previousmonth or week or hour or other time period. Or some functionrepresenting a way of weighting period of access could be employed (forexample, weighting hits as a declining exponential of days beforepresent). Thus, site sponsors can watch the activity of their web sites.The weighting period could even be reduced to minutes so that sponsorscould watch the immediate activity on their sites.

[0102] (4) Databases. Data bases that are expressible by trees can bedisplayed and searched. For example, the 7000 node taxonomic databaseused for competitive tests by ACM/SIGCHI is shown in FIG. 10. Thiscompetition is described in the publication Mullet, K., Fry, C.,Schiano, D., “On Your Marks, Get Set, Browse!” in Human Factors inComputing Systems, CHI '97 (Extended Abstracts) 1997, Atlanta Ga. ACM.In this competitive test, contestants present visualizations of thedatabase which are then searched to find particular data items. Byfollowing the higher level groupings, the user has found the node 1001entitled “Ebola Virus”. An advantage of using the DOI Tree for searchingis the entire tree is always visible which helps the user maintain thecontext of individual nodes. Also related relevant nodes are alwaysgiven more space in the standard layout while the user is browsing thetree. The automatic expansion below the focus node can help understandthe branch of the tree that contains the new focus.

[0103] (5) Multilinked databases. The nodes can be items in a databaseas in FIG. 11. The items in the database are coerced or otherwiseconverted into a tree structure. However, the items in the database havemultiple links to other items in the database. One set or class of linksis used to create the tree structure. Typically, this class of linkswill be indicative of some relationship between those items. In thisapplication, additional links to other items may be displayed when apredetermined user action is performed, e.g. a user moving a cursor overany item. This is illustrated by the links 1102 on item 1101.

[0104] In another way of presenting a general graph with multiple links,multiple instances of a node may be presented in the structure. This maybe based on a particular manner of creating the structure from thedatabase. In this case, the displayed links may point to other instancesof the node. Such duplicated nodes may be displayed so that they arevisually distinct from other nodes (e.g. by different color, shapeetc.).

[0105] By using these techniques, complex structures that would bedifficult to plot as generalized graphs are plotted as trees, but theother linkages can still be investigated. In the case where some of thenodes are aggregated together with a triangle under a node the line isdrawn to the triangle.

[0106] (4) Bibliographies. A biblioplex as described in co-pending U.S.application Ser. No. 09/488,563 filed Jan. 21, 2000, is a set ofdocuments described generated by traversing successive generations ofcitations as in FIG. 12. This can be displayed as a DOI tree. The DOIfor individual nodes can be computed through spreading activation amongthe linkages (see U.S. Pat. No. 5,895,470) or through cocitationanalysis (see U.S. Pat. No. 6,038,574).

[0107] (5) Email streams visualization. Email streams can be representedas trees. The DOI for these streams could be generated based on thecontent similarity and tree closeness.

[0108] Control Panel

[0109]FIG. 3 illustrates a control panel 1301 that may be presented to auser and used to provide visualization preferences, as well as tospecify a search term (field 1302). In the currently preferredembodiment of the present invention, there can be more than one focusnode. Typically, this would occur when some type of search is performedagainst the data in the items of the visualization structure.

[0110] Referring back to FIG. 13, the various other controls includefields and checkboxes for specifying parameters for the visualizationand command buttons for causing specific commands to be carried out.Field 1303 provides for specifying the size of the display area, field1304 provides for specifying the number of child nodes to be displayedbefore folding, field 1305 specifies an image to be used for the “box”representing a node, field 1306 is used to specify the color of the box,field 1307 is used to specify a transition time for animation purposes,field 1308 is used to specify the “fade” value for determining the finalDOI value used when rendering a node, field 1309 is used to specify amaximum DOI value before elision, field 1310 is used to specify abackground image for the visualization, field 1311 is used to specifythe color for lines and text, field 1312 is used to enable thespecification of a new root node, checkbox 1313 is used to specify thatnode expansion should occur, checkbox 1314 is used to specify thatphotos can be displayed, checkbox 1316 is used to specify that the DOIvalue for the nodes should be displayed, checkbox 1315 is used tospecify that selected nodes should be suppressed, checkbox 1317 is usedto specify that non-selected nodes are to be suppressed, checkbox 1318is used to Allow a Query, checkbox 1319 is used to specify suppressionof Low Medium nodes, checkbox 1320 is used to turn sound on or off,checkbox 1321 is to enable the user assignment of DOI values.

[0111] Button 1322 is for traversing forward through the tree based onprior commands, Button 1323 is for traversing backward through the treebased on prior commands, button 1324 is for displaying all the nodesthat had been previously selected, button 1325 is for clearing thememory of previously selected nodes, button 1326 is for causingselection of all the nodes, button 1327 is for resetting any memory ofpreviously entered commands, button 1328 is for causing the tree to beredrawn, button 1329 is for causing the tree to be drawn with largerblocks, button 1330 is for causing the tree to be drawn with smallerboxes, button 1331 is for causing the tree to be drawn with wider boxes,button 1332 is for causing the tree to be drawn with narrower boxes,button 1333 is for causing the tree to be drawn with taller boxes,button 1334 is for causing the tree to be drawn with shorter boxes,button 1335 is for causing the current focus node to be the root node,button 1336 is for causing a visualization of a subtree based on thecurrent focus node to be displayed, and button 1337 is for causingselected nodes to be deleted.

[0112] An alternative implementation would provide for certainfrequently used control functions to be presented on a tool barpositioned within the window or display area. Use of toolbars is wellknown in the art of user interfaces for computer based systems.

[0113] Software System Configuration.

[0114]FIG. 14 is a block diagram illustrating the functional componentsand data flow of the currently preferred embodiment of the presentinvention. Referring to FIG. 14, the DOITreeApp 1405 is the mainprogram. It can either be implemented as a Java program or can be anapplet. An applet is a piece of software code that is typically intendedfor execution in a Web Browser. As mentioned above, the currentlypreferred embodiment of the present invention is implemented using theJava® programming language for operation on a Java® enabled web browser.Thus, the currently preferred embodiment is implemented as an applet.The DOITreeApplet interface 1410 defines an interface for other commonlyused and publicly available applet functions that are used to implementthe DOITree system such as playAudioClip, showDocument, getlmage, etc.

[0115] DOITreeApp 1405 starts DOITree 1406 providing it with aDOITreeModel 1407. The DOITree Model 1407 defines the data to be usedfor creating the tree. The model contains a set of DOITreeNodes 1408 ina hierarchical structure. The data for each node is read from a datafile 1401 using a utility such as loadData 1404 that usesReadSpreadsheet 1402 ReadDS 1403 or other input routines depending onthe format of the data. The manner in which the data file 1401 iscreated is described in greater detail below. ReadSpreadsheet 1402 usesan input format where the data for each node is on a line in a text fileand fields of data are tab delimited. This is a format that can beproduced by commercially available spreadsheet or database software.

[0116] Once DOITree 1406 is started, it receives input from the user viamouse or keyboard controls. DOITree 1406 determines the layout, size andposition of nodes in the tree displays. DOITree 1406 callsDOITreeCellRenderer 1409 to draw each node on the display 1411 and alsoconnecting lines, images and other text or graphics on the display 1411.

[0117] In the currently preferred embodiment, the software is organizedin such a way that the main layout program element and renderer (DOITree1406 and DOITreeCellRenderer 1409) can be imbedded into other softwareand treated as a viewer for tree data. Programming in the Javaenvironment would be well known to one of skill in the art and thus nofurther discussion or description of the programming techniques used toimplement the currently preferred embodiment is deemed necessary.

[0118] As noted above, the underlying data is stored in data file 1401.In the currently preferred embodiment, this data represents the basicstructure used to display the visualization. Such data can be static orgenerated dynamically in whole or in part. The data for DOI Trees can bestored in and derived from a database or it can also be read fromtab-delimited files. Users can thus prepare and edit trees for DOI Treedisplay by using a spreadsheet application, such as Microsoft Excel®,and saving the entered data as a tab-delimited file. In a tab-delimitedfile, the tabs will indicate a separation of data items and nodeinformation.

[0119] It should also be noted that the tree may be built interactively,so that nodes may be dynamically added or removed from the treestructure. Also, such a tree structure may be built interactively byextracting information from a database responsive to user inquiries.

[0120] Overview of Computer Based System

[0121] A computer based system on which the currently preferredembodiment of the present invention may be implemented is described withreference to FIG. 15. The currently preferred embodiment of the presentinvention has been implemented on computer based systems using theWindows® Operating System and the Internet Explorer® Browser Application(both Trademarks of Microsoft Corporation of Redmond, Wash.). As notedabove, the present invention is implemented using software programminginstructions written in the Java® programming language for execution ona computer based system. Java is a trademark of Sun Microsystems ofMountain View, Calif. Thus, it is anticipated that the currentlypreferred embodiment of the present invention may operate on anycomputer based system supporting a Graphical User Interface and the JavaOperating environment. In any event, referring to FIG. 15, the computerbased system is comprised of a plurality of components coupled via a bus1501. The bus 1501 may consist of a plurality of parallel buses (e.g.address, data and status buses) as well as a hierarchy of buses (e.g. aprocessor bus, a local bus and an I/O bus). In any event, the computersystem is further comprised of a processor 1502 for executinginstructions provided via bus 1501 from Internal memory 1503 (note thatthe Internal memory 1503 is typically a combination of Random Access andRead Only Memories). Instructions for performing such operations areretrieved from Internal memory 1503. Such operations that would beperformed by the processor 1502 would include the processing stepsdescribed in the flowchart of FIG. 1 and the accompanying descriptions.The operations would typically be provided in the form of codedinstructions in a suitable programming language using well-knownprogramming techniques. The processor 1502 and Internal memory 1503 maybe discrete components or a single integrated device such as anApplication Specification Integrated Circuit (ASIC) chip.

[0122] Also coupled to the bus 1501 are a keyboard 1504 for enteringalphanumeric input, external storage 1505 for storing data, a cursorcontrol device 1006 for manipulating a cursor, a display 1507 fordisplaying visual output and a network connection 1508. The keyboard1504 would typically be a standard QWERTY keyboard but may also betelephone like keypad. The external storage 1505 may be fixed orremovable magnetic or optical disk drive. The cursor control device1506, e.g. a mouse or trackball, will typically have a button or switchassociated with it to which the performance of certain functions can beprogrammed. The display 1507 may comprise one or more physical displaymonitors. The network connection 1508 provides means for attaching to anetwork, e.g. a Local Area Network (LAN) card or modem card withappropriate software. Besides communication access, the networkconnection 1508 may be used to access various resources (i.e. servers)such as shared computing, storage or printing resources.

[0123] The invention has been described in relation to softwareimplementations, but the invention might be implemented with specializedhardware built to operate in a systems architecture as described above.

[0124] Although the invention has been described in relation to variousimplementations, together with modifications, variations, and extensionsthereof, other implementations, modifications, variations, andextensions are within the scope of the invention. The invention istherefore not limited by the description contained herein or by thedrawings, but only by the claims.

What is claimed is:
 1. A method for displaying hierarchically linkedinformation, said hierarchically linked information comprised of aplurality of nodes each having one or more links to other of saidplurality of nodes, said method comprising the steps of: a) identifyinga focus node for said plurality of nodes; b) generating a degree ofinterest (DOI) value for each of said plurality of nodes, said degree ofinterest value relative to said focus node and corresponding to a nodesize; c) laying out said plurality of nodes positioned based onassociated links and sized based on associated degree of interest valuesin a tree structure; d) identifying and performing any node compressionnecessary for displaying said hierarchically linked information based onthe layout of said plurality of inodes; and. e) displaying saidhierarchically linked information based on said layout of plurality ofnodes and node compression on a display area.
 2. The method as recitedin claim 1 further comprising the step of: f) detecting that a user hasselected a second focus node; g) generating a second degree of interestvalue for each of said plurality of nodes relative to said second focusnode; h) repeating steps c)-e) using said second degree of interestvalue for each of said plurality of nodes.
 3. The method as recited inclaim 1 wherein said step of generating a degree of interest (DOI) valuefor each of said nodes is further comprised of the steps of: b1)assigning a DOI value of 0 to focus node and parents up to root of tree;b2) assigning a DOI value of 0 to most interesting child node at userdefined number of levels below focus node; b3) assigning a DOI value of−1 to siblings of nodes with value 0; and b4) assigning a DOI value ofone less than parent for all the rest of the nodes.
 4. The method asrecited in claim 1 wherein said step of generating a degree of interest(DOI) value for each of said nodes is further comprised of the steps of:b1) assigning a DOI value of −1 to all selected nodes; b2) assigning aDOI value of −1 to parents of selected nodes up to root of tree; and b3)assigning a DOI value of one less than parent for all the rest of thenodes.
 5. The method as recited in claim 1 wherein said step of layingout said plurality of nodes positioned based on associated links andsized based on associated degree of interest values in a tree structureis further comprised of the steps of c1) determining if said structurewill fit vertically into said display area; c2) if said layout does notfit into said display area, reducing node spacing and/or sizesproportionally until node-link structure fits in said display area. 6.The method as recited in claim 1 wherein said step of identifying andperforming any node compression necessary for displaying said linkedinformation based on the layout of said plurality of nodes is furthercomprised of the steps of: d1) determining from said layout that saidnodes will not fit horizontally into said display area; and d2) causingnodes at the edges of the display area to be overlapped.
 7. The methodas recited in claim 1 wherein said step of identifying and performingany node compression necessary for displaying said linked informationbased on the layout of said plurality of nodes is further comprised ofthe step of: d1) determining from said layout that said nodes will notfit horizontally into said display area because certain levels are toowide; and d2) causing sibling nodes at wide levels to be folded intomultiple rows in the display area.
 8. The method as recited in claim 1wherein said step of identifying and performing any node compressionnecessary for displaying said linked information based on the layout ofsaid plurality of nodes is further comprised of the step of: d1)determining from said layout that said nodes will not fit verticallyinto said display area; d2) identifying subtrees in said layout causingsaid layout not to fit in said display area; d3) causing said subtreesto be displayed in a manner proportionate to the size of the subtree. 9.The method as recited in claim 1 wherein prior to step e) performing thesteps of: determining that there is unused display area for saidstructure; identifying most interesting nodes for utilizing said unuseddisplay area; and generating new degree of interest values for saididentified most interesting nodes and their linked decedent nodes. 10.The method as recited in claim 1 wherein said step of displaying saidlinked information is further comprised of the step of displaying afirst set of data items associated with said nodes.
 11. The method asrecited in claim 10 further comprising the step of: detecting that auser has requested that a second set of data items associated with saidnodes be displayed; and displaying said second set of data itemsassociated with said nodes.
 12. The method as recited in claim 11wherein said nodes are displayed to appear as three-dimensional objectshaving a plurality of display surfaces and said step of displaying saidsecond set of data items associated with said nodes is comprised of thestep of animating movement of said node to display a second surface ofsaid node having said second set of data items.
 13. System for browsinga collection of hierarchically linked data comprising: display meanshaving a display area for presenting views of a visualization of saidcollection of hierarchically linked data; input device for providinginput to change view of said visualization of said collection of linkeddata; and visualization processing element coupled to said display meansand said input device, said visualization for creating a tree structurevisualization of said collection of hierarchically linked data based ona Degree of Interest and a size of said display area.
 14. The systems asrecited in claim 13 wherein said visualization processing element isfurther comprised of: a Degree of Interest (DOI) calculation element; anode layout element; and a node compression element.
 15. The systems asrecited in claim 14 wherein said visualization processing element isfurther comprised of a node expansion element.
 16. A program storagedevice readable by a machine, tangibly embodying a program ofinstructions executable by the machine to perform method steps fordisplaying hierarchically linked information, said hierarchically linkedinformation comprised of a plurality of nodes each having one or morelinks to other of said plurality of nodes, said method comprising thesteps of: a) identifying a focus node for said plurality of nodes; b)generating a degree of interest (DOI) value for each of said pluralityof nodes, said degree of interest value relative to said focus node andcorresponding to a node size; c) laying out said plurality of nodespositioned based on associated links and sized based on associateddegree of interest values in a tree structure; d) identifying andperforming any node compression necessary for displaying saidhierarchically linked information based on the layout of said pluralityof nodes; and e) displaying said hierarchically linked information basedon said layout of plurality of nodes and node compression on a displayarea.